1. Field of the Invention
The present invention relates to an electron-beam lithographic apparatus which is arranged to write a predetermined pattern over the surface of a plate by means of an electron beam under blanking control, and more particularly to a novel electron-beam lithographic apparatus having main pattern-writing functions which can be employed to perform checking operations with respect to a written pattern.
2. Description of the Prior Art
A so-called optical transfer method in which a circuit pattern is optically transferred on a wafer has heretofore been known as a typical method of producing semiconductor integrated circuits such as LSIs on a mass scale. In this optical transfer method, a photomask or a reticle (hereinafter referred to generically as a "mask") is commonly utilized.
Electron-beam lithographic apparatus are widely used as a typical form of mask producing machine, such apparatus being characterized in that fine patterns can be written rapidly and with high precision. In this case, it is well known that the quality of masks employed determines the quality of LSIs or other devices which are obtained. Therefore, patterns written on a mask are normally checked irrespective of whether the mask producing machine employed is one of the aforesaid electron-beam lithographic apparatus.
In general, a conventional type of electron-beam lithographic apparatus is arranged such that the electron beam emitted from an electron gun thereof is placed under blanking control and at the same time under deflection control so as to write a predetermined pattern based on source data input over the surface of a plate such as a chrome coated glass covered with a photosensitive resist.
Also, in order to check masks obtained through the processings such as development and etching of plates containing written patterns, it is common practice to employ a die-to-die comparing type of checking machine, a data-base comparing type of checking machine or a scanning electron microscope.
However, when masks are to be produced using the aforesaid electron-beam lithographic apparatus and checking machine of the prior art, the following problems occur.
(1) The aforesaid die-to-die comparing type of checking machine is arranged such that, as the patterns of adjacent dies disposed on a mask are imaged through two optical systems at the same time, video signals thus obtained are compared If any disagreement is detected between the video signals, it is judged that the mask has a defect. Accordingly, this die comparing type of checking machine has a critical disadvantage in that, if any defect is contained in two video signals which are coincident with each other, it is impossible to detect such a defect. The aforesaid data-base comparing type of checking machine is typically arranged such that an optically imaged mask pattern is compared with the relevant design data by means of an electronic circuit. Thus, its detecting accuracy depends upon the configurations to be compared with each other. In addition, these machines employing optical image pick-up systems involve optical limitations such as optical wavelength and depth of focus as well as problems derived from the production of lenses Therefore, the minimum size of a defect which can be detected by the former type of checking machine is about 0.2 .mu.m while the minimum size in the case of the latter machine is about 0.3 .mu.m.
Although a checking machine of the type to which a scanning electron microscope is applied has heretofore been proposed, such a checking machine has a problem in that it imposes an excessively heavy burden on the user in an economical sense.
(2) As described above, the checking machine of the prior art involves disadvantage in that it is impossible to check a written pattern of 0.1 .mu.m or less which might be produced by a lithographic apparatus with increased accuracy. In addition, since the checking machine and the lithographic apparatus are normally disposed in separate relationship, productivity with respect to the production of masks is extremely low. As a matter of course, costs and expenses incurred by equipment increase and a space for installation also increases.
(3) Since the checking machine and the lithographic apparatus are normally arranged in separate relationship, if each machine or apparatus uses different type of machine data, it is necessary to modify the procedures and method for converting source data or intermediate format data to corresponding machine data. Accordingly, an extremely prolonged period is required for data preparation, and in addition, errors in data discrimination may occur. This could lead to a problem in that it becomes difficult to ensure the detecting accuracy of the checking machine.